In which metabolic state does PFK-2 increase Fructose 2,6-bisphosphate, thereby activating PFK-1?

In the fed state, the body is actively processing nutrients, particularly carbohydrates, leading to an increase in insulin levels. Insulin plays a crucial role in promoting glycolysis, the metabolic pathway that converts glucose into pyruvate, generating energy. One of the key regulatory steps in glycolysis is catalyzed by phosphofructokinase-1 (PFK-1), which is activated by fructose 2,6-bisphosphate.

Fructose 2,6-bisphosphate is synthesized from fructose 6-phosphate by the enzyme phosphofructokinase-2 (PFK-2). In the fed state, increased insulin levels stimulate PFK-2, resulting in higher concentrations of fructose 2,6-bisphosphate. This molecule acts as a potent activator of PFK-1, thus enhancing glycolytic flux. As a result, the overall effect is to promote glucose utilization and energy production, reflecting the body's need to metabolize the incoming nutrients efficiently.

This mechanism is critical for understanding how the body regulates energy production in response to dietary intake. In contrast, during fasting or starvation states, energy demands are met through gluconeogenesis and fatty acid oxidation, rather than glycolysis